1. Field of the Invention
The present invention relates to video processing, and, in particular, to testing the closed caption processing of televisions and other video playback devices.
2. Description of the Related Art
Closed captioning (CC) refers to the display of alphanumeric characters over the video content of a television or other video signal when rendered on a display (e.g., a television set or a computer monitor). Electronics Industries Alliance standard EIA-608 specifies requirements for embedding CC data into analog television signals. In order to determine whether conventional analog television sets are capable of proper processing of CC data, special sequences of analog television signals have been developed to verify proper closed caption processing with regard to such characteristics as the location of the CC window on the video display, the individual characters presented in the CC window, and the colors of both the characters (i.e., foreground color) and the window itself (i.e., background color).
The EIA-708-B standard specifies requirements for embedding CC data into digital television signals (i.e., DTV bitstreams). The Consumer Electronics Association (CEA) R4.3 Television Data Systems Subcommittee Working Group 1 on DTV Closed Captioning describes special DTV bitstreams for testing the closed captioning interpretation of DTV television sets and other DTV decoder.
FIG. 1 shows a block diagram of a system 100 for testing the closed caption processing of a device under test (DUT), e.g., a digital television set. As shown in FIG. 1, a bitstream source 102 provides a special DTV test bitstream with embedded CC data to DUT 104, which processes the test bitstream to generate test image data for display on display device 106, where the test image data corresponds to the video portion of the DTV signal overlaid with the closed caption portion. An observer determines whether DUT 104 is properly processing (i.e., interpreting) the CC data by viewing the test images 108 rendered on display device 106.
Bitstream source 102 may be a computer or other processor having a test bitstream stored in a memory or storage device therein or may simply be a reader of a test bitstream stored on a storage medium, such as a floppy disk, magnetic tape, a compact disk (CD), digital video disk (DVD), or other storage medium. Source 102 may also be a processor that receives test images in either analog or digital format and codes such images to form the test bitstream. In any case, DUT 104 decodes the test bitstream in accordance with the decoding circuitry and/or software and/or algorithms therein, and produces there from test image data that is applied to a display device 106, such as a television receiver, television monitor, computer display, or other visual display, to produce test images 108 thereon.
FIG. 2A shows an exemplary test image 200A generated on display device 106 during closed caption testing as specified by the CEA R4.3 working group. Test image 200A has two associated video windows 202 and 204, where the closed caption content is rendered over video window 202, and video content representative of the closed caption content is displayed in video window 204. In test image 200A, the individual CC character blocks 206 are represented by closed caption data encoded in the input DTV bitstream, while the rest of the display is part of the video data encoded in the input DTV bitstream. FIG. 2B shows the corresponding test image 200B when closed caption processing is turned off. Test image 200B of FIG. 2B is identical to test image 200A of FIG. 2A, except that, instead of displaying CC character blocks 206 within video window 202, test image 200B shows the video imagery that would otherwise be overwritten by the CC character blocks. During closed caption testing, the observer determines whether DUT 104 is operating properly by verifying that the closed caption characters in video window 202 match the video characters in video window 204. While the content in video window 204 is intended to represent the CC characters, there is no attempt to represent those characters using the same font or the same color as the CC characters. Nor is the position of CC character blocks 206 in the test image represented in the video content.
The closed caption testing specified by the CEA R4.3 working group for DTV bitstreams is directed to the same types of characteristics as the conventional closed caption testing of analog television signals.